Circuit and series resistance for indirectly heated cathodes



June 20, 1939.

F. SCHROTER CIRCUIT AND SERIES RESISTANCEFOR INDIRECTLY HEATED CATHODESFiled July 3, 1934 INVENTOR F/P/TZ S 675/ ATTORNEY Patented June 20,1939 PATENT OFFICE CIRCUIT AND SERIES RESISTANCE FOR IN- DIRECTLY HEATEDCATHODES Fritz Schriiter, Berlin, Germany, assignor to TelefunkenGesellschaft fiir Drahtlose Telegraphic m. b. 11., Berlin, Germany, acorporation of Germany Application July 3, 1934, Serial No. 733,540 InGermany July 10, 1933 2 Claims.

The present invention is concerned with radio apparatus and moreparticularly with such apparatus employing thermionic tubes havingindirectly heated cathodes.

The invention has for its main object to reduce the time of. heating ofindirectly heated cathodes (i. e. cathodes having an insulated filamentwithin a ceramic tube provided with a nickel or copper sleeve as carrierfor the emitting oxide layer) such thermal inertia, that it remains atfirst rela-' tivelycold at the beginning of the heating period. Thevoltage drop across it thus is essentially reduced, and thevoltageapplied to the heating elements of the individual indirectlyheated cathodes is therefore essentially increased over the final state,reached after complete heating. In this manner the transformation ofenergy at the cathodes is temporarily increased and therefore the timeof heating reduced.

The series resistance maybe produced for instance in the shape of. abulb, having a tungsten wire within the evacuated or gas-filled innerspace, and which is suitably mounted on a heat resisting,non-conducting, and heat removing base, or a highly effective thermicconduction is provided therefor in another physical manner. Thedimensioning of the thickness and length of the wire and of theconduction or radiation as well as the heat capacity of the entirestructure is such that the tungsten wire remains at first comparativelycold as a result of the cooling by current is supplied to the receivingtubes, and.

which accelerates the heating oi the cathodes.

Due to the excess current, the temperatiu'e of the series resistancewill also increase more rapidly, and its voltage drop finally will reachthe final value of l50 volts, while the voltage at the cathodes willdrop to '70 volts. The invention is 5 also applicable to individualcathodes of tubes connected in parallel; in this case, a single seriesresistance is possibly used, after which the heating line'is branchedoff to the cathodes. The figure shows an embodiment of the inventionby10 way of. example. Herein is i the bulb, containing the seriesresistance 2 of the shape of a helix or double helix and mounted on aceramic support of suitable dimensions. The thermic contact with thelatter can be augmented by cover- 15 ing the tungsten wire with suitablelayers such as aluminum-oxide,establishing at the same time the heatconducting connection. The cathodes schematically represented, of thereceiving or amplifying tubes 3, 4, 5 are placed in series to 20 theseries resistance.

I claim:

1. An improvement in signalling apparatus and the like of the typeprovided with at least one electronic tube having an indirectly heated25 cathode and a cathode heating circuit and wherein the cathode heatingcircuit is provided with means for connection thereof to a source ofcurrent, said improvement comprising a resistance structure connected insaid heating circuit, 30 said-structure co prising a wire resistanceelement composed o a material having a positive temperature coeflicientof resistance, said wire bei'ng' wound around a ceramic mass, saidresistance wire being provided with an outer coat- 35 ing of a good heatconducting material for estab-' lishing good heat transfer between thewire resistance and the ceramic mass, said filament and ceramic massbeing enclosed within an envelope, said ceramic mass and resistance wirebeing pro- 40 'portioned with respect to each other so that the heatcapacity of the entire structure delays for an appreciable period oftime the full efiect ofv the resistance in said circuit whereby an abnormal voltage is applied to the cathode heating 45 circuit at thebeginning of the heating period, said voltage dropping to normal at theend of said period-of delay.

2. An improvement in signalling apparatus and the like of the typeprovided with at least one electronic tube having an indirectly heatedcathode and a cathode heating circuit which-is provided with means iorconnection thereof to a source of heating current; said improvementcomprising a variable resistance device connectit ed in'the heatingcircuit saiddevice including a resistance element in series in saidheating cir-' cuit, an envelope for enclosing said wire resistance andceramic support, said ceramic support and resistance element beingproportioned with respect to each other sothat the heat capacity oftheentire structure delays for an appreciable period of time the fullefiect of the resistance .in said circuit whereby an abnormal voltage isapplied to the cathode heating circuit at the beginning of the heatingperiod, said voltage dropping to a normal value at the end of saidperiod of delay.

FRITZ SCHRCSTER.

